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The human body contains 4 to 6 liters of blood, which is about 8 percent of the total mass of the body. As the figure at right shows, about 45 percent of the volume of blood consists of cells, which are suspended in the other 55 percent—a straw-colored fluid called plasma. Plasma is about 90 percent water and 10 percent dissolved gases, salts, nutrients, enzymes, hormones, waste products, and proteins called plasma proteins.
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Blood Composition
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Plasma proteins, which perform a variety of functions, are divided into three groups: albumins, globulins, and fibrinogen. Albumins and globulins transport substances such as fatty acids, hormones, and vitamins. Albumins also help to regulate osmotic pressure and blood volume. Some globulins fight viral and bacterial infections. Fibrinogen is the protein responsible for the ability of blood to clot.
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